Method and apparatus in connection with measuring the heartbeat rate of a person

ABSTRACT

The present invention relates to a method and apparatus in connection with measuring the heartbeat rate of a person. In the method, the ECG signal of the person and the timing moment of at least one ECG signal waveform, such as the QRS complex, are measured with a heartbeat rate monitor. The average heartbeat rate frequency of the heartbeat rate is calculated from the ECG signal. Heartbeat rate variation information proportional to the magnitude of the heartbeat rate variation or to that of the total or partial power of a spectrum derived from the heartbeat rate is provided by means of a mathematical function. The heartbeat rate variation information is displayed on the display of the heartbeat rate monitor together with the average heartbeat rate frequency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus in connectionwith measuring the heartbeat rate of a person.

2. Brief Description of the Prior Art

Heartbeat rate measurement is based on monitoring cardiac function. Whencontracting, a heart produces a series of electric pulses, which can bemeasured in a body. The measurement and analysis of such a signal isreferred to as electrocardiography (ECG). The actual signal is referredto as an ECG signal. In an ECG signal, it is possible to distinguishphases resulting from different operational stages of the heart. Theseportions are the so-called P, Q, R, S, T and U-waves.

In known solutions, a heartbeat rate monitor shows on its display mainlyaverage heartbeat rate information only, which is calculated as anaverage from a suitable number of single pulsations. However, there isneed to render the heartbeat rate monitors more versatile. In existingheartbeat rate monitors which filter heartbeat rate, the averaging whichlevels instantaneous heartbeat rate variation prevents the heartbeatrate measurement information from being analyzed in more detail. Insignal processing, averaging means low pass filtering, which as used inthis connection cuts the fast variation signal away from the heartbeatrate signal. The known solutions do not provide sufficientlymulti-faceted information.

Due to the variation in the sympathetic-parasympathetic balance of theautonomic nervous system, variations around the average heartbeat ratelevel occur constantly in heartbeat rate. The variation in heartbeatrate is caused by the function of the cardiovascular control system. Themain reasons for the variation are respiratory arrhythmia, variationcaused by blood pressure control, and variation caused by the heatbalance control of the system. Among these, the most significant andcausing the greatest variation is respiratory arrhythmia. Thetransmitting nervous systems of heartbeat rate variation can bedistinguished by means of heartbeat rate variation frequency analysis.At the present time, the sympathetic nervous system is considered to beslow; it is hardly capable of transmitting frequencies higher than 0.15Hz. Instead, the operation of the parasympathetic nervous system isfast, wherefore frequencies higher than the above-mentioned thresholdfrequency are transmitted through the parasympathetic nervous system.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a new type of methodand apparatus, with the use of which the problems associated with theknown solutions are avoided.

The invention is characterized by what is defined in the claims below.

Many advantages are achieved with the invention. Measuring heartbeatrate variation and showing the measurement result on the display of theheartbeat rate monitor provide important additional information on theoperation of a human body and nervous system, especially on the degreeof relaxation of a human. By using heartbeat rate variation according tothe invention for defining the degree of relaxation, it is possible toimplement individual monitoring which is sufficiently multi-faceted andaccurate for the needs of a person. The invention thus enables real-timeand wireless monitoring of heartbeat rate variation, whereby theinvention provides us with more information without difficultmeasurements carried out in laboratories. A great heartbeat ratevariation is an indication that the parasympathetic nervous systemfunctions, which generally corresponds to a relaxed state of a system.As for a small value, it indicates that the sympathetic nervous systemis active, which is related to physical or mental stress. Thus, bymeasuring heartbeat rate variation, it is possible to monitor the stateof the autonomic nervous system.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail bymeans of examples with reference to the accompanying drawings, in which

FIG. 1 shows the shape of an ECG signal caused by heartbeat rate,

FIG. 2 shows a heartbeat rate variation graph during exertion,

FIG. 3 shows a general view of the apparatus of the invention,

FIG. 4 shows a functional diagram of the apparatus according to anembodiment of the invention,

FIG. 5 shows the display of a heartbeat rate monitor,

FIGS. 6a-6e show the forming of a heartbeat rate variation signal froman ECG signal.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a typical ECG signal caused by heartbeat rate as presentedin a time-voltage coordinate system. The above-mentioned P, Q, R, S, andT-waves can be distinguished in each signal by an accurate measurement.The highest value R represents the maximum point of an ECG signal, andthe pulsation defined by the points Q, R and S, i.e. the QRS complex,represents the most easily distinguishable part of the ECG signal. Theinterval between two successive R peak values is often referred to asthe R--R interval of the ECG signal. A P-wave is caused by thecontraction of the atria. When the atria contract, the ventricles arefilled with blood. The QRS complex formed by the peaks of three waves,defining the shape of the R peak of the ECG signal, is produced when theventricles contract. The right ventricle thus pumps blood from veins tothe lungs, and the left ventricle pumps blood from the lungs toarteries. The repolarization of the ventricle muscles causes a T-wave,which is lower and more even than the R peak. The periods between thewaves depend on the speed of propagation of the nervous stimulus in theheart.

In a healthy human, the ECG signal is between 1 and 2 mV in amplitude asmeasured on the skin. For instance, the amplitude value and durationgiven for an R peak in literature are 1.6 mV and 90 ms, whereas thecorresponding values for a P-wave are 0.25 mV and 110 ms. When theheartbeat rate accelerates as a result of exertion, the durations andamplitudes of the different components of the ECG signal remain almostunchanged. It is thus known that the accurate measurement of heartbeatrate and related phenomena is possible by analyzing the ECG signal ofheartbeat rate.

The easiest starting point for determining the timing point of an ECGsignal accurately is the detection of the QRS complex. In adisturbance-free situation, the QRS complex can be detected in a fairlysimple manner by means of a peak value detector. To reduce the number ofdisturbances occurring in practical situations, some type of filteringis used in accurate analyses. The filtering may take place by using aband-pass filter, adapted filter, or pattern recognition.

FIG. 2 shows the behaviour of heartbeat rate variation according to thelevel of exertion. The graph is drawn on the basis of standarddeviations calculated from 100 successive R--R intervals. The figureshows a distinct non-linear decrease in the variation when the exertionis increased.

In the method of the invention, an ECG signal is measured at the chestor some other body part of a person engaged in exercise, and this signalis transmitted to a receiver as in existing heartbeat rate monitors. Theresolution of the heartbeat rate transmitter in defining the timinginformation of successive ECG signals is at least in the range of 1 ms.The heartbeat rate of the exercising person is constantly monitoredduring the entire performance. The heartbeat rate monitor measures, asdeviating from averaging monitors, some unambiguous timing point of eachECG signal, for instance the R--R interval obtained from QRS complexes,and calculates the standard deviation of the heartbeat rate or someother variation index from the collected intervals. The heartbeat ratemonitor constantly monitors the development of the variation.

FIG. 3 shows a schematic view of the exemplifying apparatus of theinvention. In the telemetric heartbeat rate monitor shown in FIG. 3, ECGelectrodes la are connected to the differential input poles of an ECGpre-amplifier 1. The heartbeat rate signal provided by the pre-amplifier1 is amplified in an AGC amplifier 2, which is used for controlling apower amplifier 3, in which is produced a heartbeat rate signalcontrolling coils 4, the interval between the pulses of the signal beingthe same as the interval between the heart pulsations. A magnetic fieldvarying with the rhythm of the heartbeat rate is thus generated in thecoils 4. The blocks 1-4 of FIG. 1 preferably constitute a telemetrictransmitter unit, such as a transmitter belt, which a person wearsagainst his skin, for instance against his chest.

In FIG. 3, the other blocks, beginning from block 5, constitute atelemetric receiver unit, which is preferably for instance a receiverwristband worn on the wrist. The magnetic field received from the coils4, detected by receiving coils 5, is amplified in a sensitivepre-amplifier 6, whereafter the signal is applied to a signal amplifier7. The output signal of the amplifier is processed in a microcomputer 8,which calculates from a desired number of previous pulses an averageheartbeat rate, which is indicated, i.e. displayed, on a display 10,such as a liquid crystal display 10 in a display element 10a. Theaverage heartbeat rate can also be stored in a memory 9. As regards theabove-mentioned elements 1-10, the apparatus corresponds to knownapparatuses.

The most essential part of the invention is a block 30 and a displayelement 40, to which the block 30 is connected. The block 30 is a meansfor calculating the heartbeat rate variation. The means 30 can beimplemented as a program segment of the microcomputer 8. The means 30calculates the heartbeat rate variation data and indicates the heartbeatrate variation in the display element 40. In practise, the displayelement 10a for indicating the average heartbeat rate and the displayelement 40 for indicating the heartbeat rate variation are differentdisplay elements included in the same display unit 10, such as a liquidcrystal display.

FIG. 4 shows a functional diagram of the apparatus according to anembodiment of the invention. The functions according to the diagram arepreferably included in the software of the microcomputer 8 of theheartbeat rate monitor. The purpose is to determine the heartbeat ratevariation of a person engaged for instance in exercise or sportstraining. In FIG. 4, the heartbeat rate measurement which is the basisof the operation is carried out in block 11. By means of the heartbeatrate monitor 5-10, the heartbeat rate of a person and the timing momentof at least one waveform of the ECG signal, for instance the QRScomplex, are measured during the training period.

Thereafter, instantaneous heartbeat rate is calculated in block 12 onthe basis of corresponding ECG signal waveform distances, and a possibleshaping is carried out for instance with a suitable digital filter. Theheartbeat rate signal can be preferably high pass filtered in thisconnection to remove slow processes distorting the result, theseprocesses being due for instance to sudden changes in load levels.

A heartbeat rate variation value proportional to the magnitude of theheartbeat rate variation or to that of the total or partial power of aspectrum derived from the heartbeat rate is provided by means of astatistical function 13, i.e. by the formula of the standard deviation Sin this example. The heartbeat rate variation can also be calculated forinstance by means of the height or width of the heartbeat rate variationdistribution pattern or by means of a quantity provided by a statisticalfunction derived from the height and width. The block 13 of FIG. 4corresponds to the block 30 in FIG. 3.

The heartbeat rate variation values calculated during the trainingperiod are registered, i.e. stored, in the memory 9 in a block 14 as atime function, and the heartbeat rate variation information is alsodisplayed on the display element 40 of the display 10. The heartbeatrate monitor of the invention thus comprises a heartbeat rate variationcalculation unit 30 and a display element 40, which displays, on areal-time basis, an index number and/or a graphic indicator proportionalto the heartbeat rate variation, for instance a bar 40, the height ofwhich is in some manner proportional to the calculated heartbeat ratevariation. FIGS. 6a-6e show examples of how a heartbeat rate variationsignal is derived from an ECG signal. The starting point is the measuredECG signal according to FIG. 1, in which a suitable timing point t_(i)(FIG. 6a) is determined on the basis of R pulses. FIG. 6b shows thedetermination of instantaneous heartbeat rate on the basis of the timingpoints t₁ . . . t_(n) of R--R intervals. The instantaneous heartbeatrate is shown as a continuous signal in an R--R time domain in FIG. 6cand in a heartbeat rate time domain in FIG. 6d, the heartbeat rateequalling 60/RR in the heartbeat rate time domain. FIG. 6e shows aheartbeat rate variation graph, which can be calculated directly fromthe R--R intervals (FIG. 6b) as a recursively floating standarddeviation, or as a moving height or width determined from the shape ofthe distribution pattern, or as a value of the partial or total power ofa spectrum derived from the signals of FIG. 6c or 6d.

In the apparatus of the invention, the heartbeat rate variation display40, i.e. a so-called relaxation display 40, preferably consists of a barcomprising for instance 10 parts. The height of the bar directlyrepresents the standard deviation of pulsation intervals. The higher thebar, the greater the standard deviation and correspondingly the degreeof relaxation.

In the preferred embodiment of the invention, the heartbeat ratevariation is indicated on the display 10 of the heartbeat rate monitorsimultaneously with the average heartbeat rate in the method. The useris thus able to detect both the average heartbeat rate and the heartbeatrate variation at the same time at a single glance, the heartbeat ratevariation thus indicating the degree of relaxation of the person.

In the preferred embodiment of the invention, the heartbeat ratevariation information is indicated on the display of the heartbeat ratemonitor graphically and/or digitally in the method. The graphic displayis implemented for instance with a bar-like display element.

The digital display can be implemented with display elements 41-42.

In the method, the heartbeat rate variation information is indicated onthe display of the heartbeat rate monitor simultaneously bothgraphically and digitally.

The heartbeat rate variation information is indicated on such a commondisplay element that is also used for indicating the modes and setconditions of the heartbeat rate monitor.

In the method, an indicator 50 indicates whether the common displayelement 40 displays heartbeat rate variation information or modes andset conditions.

Even if the invention has been described above with reference to theexamples according to the accompanying drawings, it will be apparentthat the invention is not so restricted, but it can modified in variousways within the scope of the inventive concept disclosed in the appendedclaims.

What is claimed is:
 1. A method in connection with measuring theheartbeat rate of a person, comprising the following steps:measuring theECG signal of the person and the timing moment of at least one ECGsignal waveform, calculating the average heartbeat rate from the ECGsignal, providing, by means of a mathematical function, real-timeheartbeat rate variation information proportional to one of themagnitude of the heartbeat rate variation, the total power of a spectrumderived from the heartbeat rate and the partial power of a spectrumderived from the heartbeat rate, and displaying in real time saidheartbeat rate variation information.
 2. A method according to claim 1further comprising the additional step of displaying the heartbeat ratevariation information simultaneously with the average heartbeat rate. 3.A method according to claim further comprising the additional step ofindicating the heartbeat rate variation information at least one ofgraphically and digitally.
 4. A method according to claim 3, wherein theheartbeat rate variation information is indicated simultaneously bothgraphically and digitally.
 5. A method according to claim 1, wherein insaid step of providing the heartbeat rate variation information, theheartbeat rate variation information is calculated by means of astatistical function which provides the standard deviation of theheartbeat rate as a result.
 6. A method according to claim 1, wherein insaid step of providing the heartbeat rate variation information, theheartbeat rate variation information is calculated by means of astatistical function which provides one of the height and width of thedistribution pattern of one of an instantaneous heartbeat rate signaland R--R signal as a result.
 7. A method according to claim 1, whereinin said step of providing the heartbeat rate variation information, theheartbeat rate variation information is calculated from a continuousheartbeat rate signal.
 8. A method according to claim 1 including thestep of constantly monitoring development of the heartbeat ratevariation.
 9. A method according to claim 1, including the steps ofgenerating a magnetic field varying with the rhythm of the heartbeatrate with a telemetric transmitter unit and detecting said magneticfield with a telemetric receiver unit, said steps of calculating theaverage heartbeat rate frequency, providing real time heartbeat ratevariation information and displaying said heartbeat rate variationinformation being performed by said telemetric receiver unit.
 10. Amethod as described in claim 9 including the steps of positioning saidtelemetric transmitter unit near the chest of the person and securingsaid telemetric receiver unit to a wrist of the person.
 11. An apparatusin connection with measuring the heartbeat rate of a person, theapparatus comprising:means for detecting and transmitting heartbeatsignals, a heartbeat rate monitor for receiving, calculating andmeasuring said heartbeat signals, and for registering the timing momentof at least one ECG signal waveform contained by a heartbeat signal,means for calculating on a real-time basis the average heartbeat rate onthe basis of the ECG signal, means for providing real-time heartbeatrate variation information proportional to one of the magnitude of theheartbeat rate variation, the total power of a spectrum derived from theheartbeat rate and the partial power of a spectrum derived from theheartbeat rate by means of a mathematical function, and means forindicating in real time the heartbeat rate variation information on theheartbeat rate monitor.
 12. An apparatus according to claim 11, whereinthe means for indicating the heartbeat rate variation information on theheartbeat rate monitor comprises a display element which also indicatesthe average heartbeat rate information.
 13. An apparatus according toclaim 11, wherein the means for indicating the heartbeat rate variationinformation comprises at least one of a graphic and digital displayelement.
 14. An apparatus according to claim 11, wherein the means forindicating the heartbeat rate variation information comprises a displayelement which also indicates modes and set conditions on the heartbeatrate monitor.
 15. An apparatus according to claim 11, further comprisinga high pass filter for filtering a heartbeat rate signal.
 16. Anapparatus according to claim 11, wherein said means for detecting andtransmitting heartbeat signals comprises a telemetric transmitter unitand said heartbeat monitor comprises a telemetric receiver unit, saidtelemetric transmitter unit including means for generating a magneticfield varying with the rhythm of the heartbeat rate, said telemetricreceiver unit including means for detecting the magnetic field generatedby the telemetric transmitter unit.
 17. An apparatus according to claim16, wherein said heartbeat rate monitor includes means for constantlymonitoring development of heartbeat rate variation.
 18. A method ofproviding information relating to the heartbeat of a person,comprising:measuring the ECG signal of the person and the timing momentof at least one ECG signal waveform, providing, from the ECG signal, apulse sequence wherein each pulse is representative of a heartbeat ofthe person, said pulse sequence having intervals between the pulses ofsaid pulse sequence, calculating on a real time basis the averageheartbeat rate from the pulse sequence derived from the ECG signal,providing, by means of a mathematical function, real time heartbeatinterval variation information proportional to one of the magnitude ofthe heartbeat interval variation, the total power of a spectrum derivedfrom the heartbeat rate and the partial power of a spectrum derived fromthe heartbeat rate, and displaying in real time said heartbeat intervalvariation information.
 19. A method as described in claim 18, whereineach pulse corresponds to an R peak of an ECG signal.
 20. A method asdescribed in claim 18 including the step of displaying said heartbeatinterval variation and said average heartbeat rate simultaneously.
 21. Amethod as described in claim 18 including the steps of detecting saidECG signal with a telemetric transmitter unit and displaying saidheartbeat interval variation information on a telemetric receiver unitworn by the person.
 22. An apparatus for measuring the heartbeat rate ofa person and providing heartbeat interval variation information,comprising:means for detecting and transmitting heartbeat signals, areceiver unit for receiving said heartbeat signals and for registeringthe timing moment of at least one ECG signal waveform contained by aheartbeat signal, and for providing from the ECG signal, a pulsesequence wherein each pulse is representative of a heartbeat of theperson, said pulse sequence having intervals between the pulses of saidpulse sequence, means for calculating on a real time basis the averageheartbeat rate on the basis of the ECG signal, means for providing realtime heartbeat interval variation information proportional to one of themagnitude of the heartbeat interval variation, the total power of aspectrum derived from the heartbeat rate and the partial power of aspectrum derived from the heartbeat rate, wherein the heartbeat intervalvariation is based on collected intervals between the pulses of saidpulse sequence, and means for indicating, in real time, said heartbeatinterval variation information.
 23. An apparatus as described in claim22, wherein said intervals between heartbeat signals correspond to theR--R intervals obtained from QRS complexes of individual ECG signals.24. An apparatus as described in claim 22, wherein said means fordetecting and transmitting heartbeat signals is a telemetric transmitterunit, said apparatus includes a telemetric receiver unit, said means forcalculating, means for providing and means for indicating beingincorporated in said telemetric receiver unit.